Prostanoids, including prostaglandin E2 (PGE2), have been implicated in the pathophysiology of a number of cardiovascular diseases. Preliminary data demonstrates that selective pharmacological inhibition of cyclooxygenase-2 (COX-2) markedly attenuates the incidence of abdominal aortic aneurysms (AAA) in mice infused with angiotensin II (AngII), suggesting that prostanoids play a critical role in the development of AAAs. Hallmarks of AAA formation are inflammation and increased expression and activation of matrix metalloproteinases (MMPs) in the vascular wall. During inflammation both COX-2 and microsomal prostaglandin E synthase-1 (m-PGES-1) are rapidly upregulated resulting in increased concentrations of PGE2. PGE2 regulates MMP expression and activation, therefore reductions in COX-2 generated PGE2 may result in decreases in MMP expression and activation. Previous studies have associated reductions in PGE2 with decreases in MMPs and aneurysmal expansion. Preliminary data demonstrates that m-PGES1 deficiency attenuates AngII-induced AAA formation. PGE2 concentrations were markedly decreased in the mPGES-1 deficient mice, however, there was a concomitant increase in prostacyclin (PGI2) concentrations. Blockade of the PGI2 receptor protects against that development of other vascular disease. Therefore, the direct role of PGE2 in mediating the development of AAAs has not been elucidated. PGE2 mediates its actions by binding to EP receptors. The EP4 receptor is expressed in aneurysmal tissues and is required for the activation MMPs. The long-term objective of this proposal is to elucidate the role of the PGE2 in AngII-induced AAA formation. We propose to test the hypothesis that mPGES-1 generated PGE2 mediates the initial stage of AngII-induced AAA formation via the EP4 receptor. To test this hypothesis we propose to: 1) define the role of mPGES-1 generated PGE2 in AngII-induced AAAs; 2) define the role of the PGE2-EP4 receptor axis in MMP expression and activation in cells implicated in the development of AAAs and; 3) determine if the EP4 receptor is critical for the development of AngII-induced AAAs. To date there are not therapeutic treatments for AAAs. With the suggestion that an increased risk for cardiovascular events is a class specific effect of COX-2 inhibitors, data from these studies will be important in defining which prostanoids generated by COX-2 mediate the initial events in AAA formation and provide us with critical information for targeting specific prostanoid synthases and receptors as therapeutic treatment for this disease.